It looks like the colors don't work when going from generic Special:RecentChanges to the localized form.

The highlights show up when changing nl to de and Speciaal:RecenteWijzigingen to Spezial:Letzte_Änderungen in the following URL.

https://nl.wikipedia.org/w/index.php?tagfilter=mentorship module question|newcomer task add link&limit=500&days=30&enhanced=1&tagfilter__newcomer task add link_color=c1&title=Speciaal:RecenteWijzigingen&tagfilter__mentorship_module_question_color=c3&tagfilter__newcomer_task_add_link_color=c1&tagfilter__newcomer_task_color=c1&urlversion=2

Moving to Needs Discussion for prioritization

@MMiller_WMF what do you need to prioritize this?

When you enter the English name on a non-English wiki, the browser gets redirected to the local name. Apparently that messes up the query parameters somewhat:

hidebots=1&hidenewpages=1&hidecategorization=1&hideWikibase=1&tagfilter=newcomer task&limit=500&days=30&enhanced=1&tagfilter__newcomer task_color=c1&tagfilter__mentorship module question_color=c3&urlversion=2
hidebots=1&hidenewpages=1&hidecategorization=1&hideWikibase=1&tagfilter=newcomer task&limit=500&days=30&enhanced=1&tagfilter__newcomer_task_color=c1&tagfilter__mentorship_module_question_color=c3&urlversion=2

(pre and post redirect, note the vs. _ as Benoît said). That's what we get for using spaces in change tag names, I suppose.

Could happen in WebRequest::getQueryValues() (called from SpecialPageFactory::executePath()), or somewhere in our infrastructure (Apache rewrite rules on the appserver hosts?) where we translate nice URLs to index.php ones.

@mewoph @Tgr -- is this bug limited only to the use case in which a user copy/pastes a RecentChanges URL from one language to another? If so, then this seems like an edge case that we would not be able to prioritize now.

Depending on where the error is, it might things other than recent changes, but for recent changes specifically, I think it would only affect that case.

It's actually PHP doing this. https://www.php.net/variables.external

Note:

Dots and spaces in variable names are converted to underscores. For example <input name="a.b" /> becomes $_REQUEST["a_b"].

Yeah that makes sense, SpecialPageFactory fetches query params via Request::getQueryValues() (which is basically just $_GET) for generating the redirect URL.

Maybe we should have a getActualQueryValues() which just parses the URL.